Sustainable bamboo–plastic composites from upcycled chopsticks and post-consumer polypropylene: Effect of feedstock origin on interfacial adhesion and properties

The sustainable management of food-service waste requires innovative upcycling strategies to mitigate environmental accumulation. This study valorizes two problematic waste streams—post-consumer polypropylene (rPP) from diverse packaging and discarded bamboo chopsticks (rB)—into high-performance bamboo-plastic composites (BPCs). The novelty of this work lies in eliminating synthetic coupling agents by utilizing endogenous oxidation products in the rPP matrix to enhance interfacial compatibility with hydrophilic bamboo fibres. Thermal analysis revealed that beverage-grade rPP exhibited a higher crystallinity (49.18%) than its food-grade and virgin counterparts. Crucially, FTIR spectroscopy identified oxidative degradation products in the recycled matrices which, rather than compromising performance, functioned as intrinsic adhesion promoters. This increased surface polarity significantly enhanced interfacial bonding with the hydrophilic bamboo fibres compared to virgin PP systems, as corroborated by scanning electron microscopy. Although the rB fibres underwent a reduction in cellulose crystallinity and increased hygroscopicity due to prior service life, the resulting composites maintained robust mechanical and physical integrity. All rPP-rB formulations successfully complied with the Thai Industrial Standard (TIS 2998-2019) for exterior-grade applications, achieving densities >0.90 g·cm⁻³, flexural strengths >20 MPa, and 24-hour water absorption <5%. These findings suggest that the cumulative thermal history and intrinsic oxidation of recycled polymers could be strategically leveraged to engineer compatible, value-added circular materials, offering a scalable route for upcycling contaminated food-service waste. • Upcycled bamboo chopsticks and post-consumer PP for sustainable BPCs fabrication. • Recycled PP shows higher crystallinity than virgin grade for beverage packaging. • Oxidized groups in recycled PP act as intrinsic interfacial adhesion promoters. • BPCs meet TIS 2998-2019 standards for exterior-grade structural applications. • Superior bonding in recycled PP-bamboo systems without synthetic coupling agents.